Co-founding ant queens prevent disease by performing prophylactic undertaking behaviour

Sylvia Cremer,Christopher D Pull

doi:10.1186/s12862-017-1062-4

Sylvia Cremer, Christopher D Pull

Open Access

https://doi.org/10.1186/s12862-017-1062-4

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Abstract

BackgroundSocial insects form densely crowded societies in environments with high pathogen loads, but have evolved collective defences that mitigate the impact of disease. However, colony-founding queens lack this protection and suffer high rates of mortality. The impact of pathogens may be exacerbated in species where queens found colonies together, as healthy individuals may contract pathogens from infectious co-founders. Therefore, we tested whether ant queens avoid founding colonies with pathogen-exposed conspecifics and how they might limit disease transmission from infectious individuals.ResultsUsing Lasius niger queens and a naturally infecting fungal pathogen Metarhizium brunneum, we observed that queens were equally likely to found colonies with another pathogen-exposed or sham-treated queen. However, when one queen died, the surviving individual performed biting, burial and removal of the corpse. These undertaking behaviours were performed prophylactically, i.e. targeted equally towards non-infected and infected corpses, as well as carried out before infected corpses became infectious. Biting and burial reduced the risk of the queens contracting and dying from disease from an infectious corpse of a dead co-foundress.ConclusionsWe show that co-founding ant queens express undertaking behaviours that, in mature colonies, are performed exclusively by workers. Such infection avoidance behaviours act before the queens can contract the disease and will therefore improve the overall chance of colony founding success in ant queens.

Highlights

Social insects form densely crowded societies in environments with high pathogen loads, but have evolved collective defences that mitigate the impact of disease
We introduced pathogen-exposed or sham-treated queens to an experimental setup where they could choose to start a nest alone, or with a pathogen-exposed or sham-treated queen already residing in the nest, using a full factorial design
We observed no effect of pathogen-exposure on the likelihood that queens co-found colonies within a 72-h observation period (Fig. 1; overall generalised linear mixed model [GLMM] comprising queen treatment, time and their interaction, n = 20 per treatment group, likelihood ratio test (LR) χ2 = 4.95, df = 7, P = 0.7)

Summary

Introduction

Social insects form densely crowded societies in environments with high pathogen loads, but have evolved collective defences that mitigate the impact of disease. Behaviour that decreases the probability of an individual acquiring pathogens should confer fitness advantages and be selected for over time [1] This is because mounting an immune response post-infection can have a severe impact on an animal’s future reproduction and survival, whilst behavioural mechanisms can negate these costs by preventing infection altogether [2,3,4,5]. In social insects (ants, termites and some bees and wasps) workers perform collective behaviours, such as grooming, which reduce the per capita risk of infection and result in colony-level disease protection, known as social immunity [14]. We might expect selection acting on queens to produce behaviours that reduce this risk

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